1. Field of the Invention
The present invention relates a method and apparatus for reinforcing pipe walls to increase their strength and ductility without removing a section of the pipe from its original position.
2. Related Art
In general, pipes either below or above ground need to be repaired after a number of years of operation due to deterioration. Existing pipes formed from steel and/or concrete have numerous problems. For example, steel pipes are prone to losing their structural integrity over time due to corrosion and concrete pipes are subject to deterioration due to permeability of the exposed concrete by water.
Previously, repairing pipes involved excavating the pipe from the ground, removing the section to be repaired and burying a new section. This process was expensive and time consuming, and also required that the pipe be out of service for a period of time. Subsequently, methods for repairing cracks and breaks in pipes have been developed whereby the pipes need not be excavated in order to be repaired. These methods include the use of inserts to act as new pipe walls.
One such method of repairing an underground pipe involves inserting a sufficiently long tubular flexible liner bag into the pipe by means of a pressurized fluid, such as air or water. The tubular liner bag is made of a flexible resin-absorbent material impregnated with a thermosetting resin, and the outer surface is covered with a water impermeable plastic film.
In particular, the tubular flexible liner bag is closed at one end and open at the other. The tubular flexible liner bag is first flattened, and then, the closed end of the tubular liner bag is tied to a control rope. The open end of the tubular liner bag is made to gape wide and is hooked (anchored) at the end of the defective or old pipe in such a manner that the wide-opened end of the liner completely and fixedly covers and closes the pipe end. A portion of the liner is pushed into the pipe. The pressurized fluid is applied to the portion of the tubular liner such that the fluid urges the tubular liner to enter the pipe. Since one end of the tubular liner is hooked at the end of the pipe, it remains there while the rest of the flexible liner bag is turned inside out as it proceeds deeper in the pipe. When the entire length of the tubular liner bag is everted (i.e., turned inside out) into the pipe, the control rope holds the closed end of the tubular liner bag to thereby control the length of the tubular liner in the pipe. The everted tubular liner is pressed against the inner wall of the pipe by the pressurized fluid. The tubular liner is hardened as the thermosetting resin impregnated in the tubular liner bag is cured.
This process enables a pipe to be repaired without excavation or disassembly. However, if the process is applied to an underground pipe into which ground water penetrates, the problem arises that the thermosetting resin impregnated in the tubular pipe liner bag may be diluted or wash out of the material before it cures. Thus, neither adequate strength of the liner nor an adequate bond between the insert liner and the pipe may be maintained. Also, during the insertion process, material may accumulate on the outside of the resin impregnated liner bag, thereby reducing available bonding surface and consequently strength and sealing capabilities of the repair. In addition, void areas where resin is not present can occur in the liner bag, thereby causing areas of weakness and areas where the liner fails to properly bond to the pipe.
Accordingly, there remains a need for an efficient and cost-effective way to adequately reinforce pipes so as to increase their resistance to structural failure due to deterioration.